Sounding and tone block allocation for orthogonal frequency multiple access (OFDMA) in wireless local area networks

ABSTRACT

A first communication device obtains, for each second communication device of a plurality of second communication devices, one or more quality indicators corresponding to one or more sub-channel blocks of an orthogonal frequency division multiplexing (OFDM) communication channel associated with the second communication device. The first communication device selects, based on the quality indicators obtained for each of at least some of the second communication devices, a group of second communication devices for orthogonal frequency division multiple access (OFDMA) communication. The first communication device transmits, to the group of second communication devices, at least one OFDMA data unit that includes respective OFDM data units directed to the two or more second communication devices of the group. The respective OFDM data units are transmitted in respective sub-channel blocks allocated to the two or more second communication devices of the group.

CROSS-REFERENCE TO RELATED APPLICATION

This disclosure claims the benefit of U.S. Provisional PatentApplication Nos. 61/909,700, filed Nov. 27, 2013, and 61/938,441, filedFeb. 11, 2014, both entitled “OFDMA for WLAN: Sounding and Tone-BlockAllocation,” the disclosures of which are hereby expressly incorporatedherein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughputs, such as throughputs in the tens of Gbps range.

SUMMARY

In an embodiment, a method for simultaneously communicating withmultiple communication devices in a communication network includesobtaining, at a first communication device for each second communicationdevice of a plurality of second communication devices, one or morequality indicators corresponding to one or more sub-channel blocks of anorthogonal frequency division multiplexing (OFDM) communication channelassociated with the second communication device. The method alsoincludes selecting, at the first communication device based on thequality indicators obtained for each of at least some of the secondcommunication devices, a group of second communication devices fororthogonal frequency division multiple access (OFDMA) communication,wherein the group includes two or more second communication devices ofthe plurality of second communication devices. The method additionallyincludes transmitting, from the first communication device to the groupof second communication devices, at least one OFDMA data unit thatincludes respective OFDM data units directed to the two or more secondcommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more second communication devices of the group.

In another embodiment, an apparatus for use in a communication systemcomprises a network interface configured to obtain, for each of aplurality of communication devices, one or more quality indicatorscorresponding to one or more sub-channel blocks of an orthogonalfrequency division multiplexing (OFDM) communication channel associatedwith the communication device. The network interface is furtherconfigured to select, based on the quality indicators obtained for eachof at least some communication devices of the plurality of communicationdevices, a group of communication devices for orthogonal frequencydivision multiple access (OFDMA) communication, wherein the groupincludes two or more communication devices of the plurality ofcommunication devices. The network interface is additionally configuredto transmit, to the group of communication devices, at least one OFDMAdata unit that includes respective OFDM data units directed to the twoor more communication devices of the group, wherein the respective OFDMdata units are transmitted in respective sub-channel blocks allocated tothe two or more communication devices of the group.

In yet another embodiment, a method for simultaneously communicatingwith multiple communication devices in a communication network includesobtaining, at a first communication device for each of two or moresecond communication devices in a group of second communication devicesfor orthogonal frequency division multiple access (OFDMA) communication,one or more quality indicators corresponding to one or more sub-channelblocks of an orthogonal frequency division multiplexing (OFDM)communication channel associated with the second communication device.The method also includes allocating, based on the quality indicatorsobtained for each of at least some of the two or more secondcommunication devices of the group, respective sub-channel blocks torespective second communication devices of the group. The methodadditionally includes transmitting at least one orthogonal frequencydivision multiple access (OFDMA) data unit that includes respective OFDMdata units directed to the two or more communication devices of thegroup, wherein the respective OFDM data units are transmitted inrespective sub-channel blocks allocated to the two or more communicationdevices of group.

In still another embodiment, an apparatus for use in a communicationsystem comprises a network interface configured to obtain, for each oftwo or more communication devices in a group of communication devicesfor orthogonal frequency division multiple access (OFDMA) communication,one or more quality indicators corresponding to one or more sub-channelblocks of an orthogonal frequency division multiplexing (OFDM)communication channel associated with the communication device. Thenetwork interface is additionally configured to allocate, based on thequality indicators obtained for each of at least some of the two or morecommunication devices of the two or more communication devices,respective sub-channel blocks to respective communication devices of thegroup. The network interface is further configured to transmit at leastone orthogonal frequency division multiple access (OFDMA) data unit thatincludes respective OFDM data units directed to the two or morecommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more communication devices of group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a block diagram of an example wireless local area network (WLAN),according to an embodiment;

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating example orthogonalfrequency division multiplexing (OFDM) sub-channel blocks for an 80 MHzcommunication channel, according to an embodiment;

FIG. 3 is a diagram of an example OFDMA data unit, according to anembodiment.

FIG. 4A is a timing diagram of an example explicit sounding procedureand transmission of an example OFDMA data unit formed according togrouping and/or channel allocation determined based on the explicitsounding procedure, according to an embodiment.

FIG. 4B is a diagram of a feedback packet that a transmitted during thesounding procedure of FIG. 4A, according to an embodiment.

FIG. 4C is a diagram of a feedback packet that a transmitted during thesounding procedure of FIG. 4A, according to another embodiment.

FIG. 5 is a timing diagram of an example implicit sounding procedure andtransmission of an example OFDMA data unit formed according to groupingand/or channel allocation determined based the implicit soundingprocedure, according to an embodiment.

FIG. 6 is a timing diagram of an example transparent implicit soundingprocedure and transmission of an example OFDMA data unit formedaccording to grouping and/or channel allocation determined based thetransparent implicit sounding procedure, according to an embodiment.

FIG. 7 is a timing diagram illustrating a notification procedure used byan AP to inform a plurality of client stations that the client stationsare members of a group of client stations for OFDMA communication,according to an embodiment.

FIG. 8 is a timing diagram illustrating a notification procedure used byan AP to inform a plurality of client stations that the client stationsare members of a group of client stations for OFDMA communication,according to another embodiment.

FIG. 9 is a flow diagram of an example method for simultaneouslycommunicating with multiple communication devices in a WLAN, accordingto an embodiment.

FIG. 10 is a flow diagram of an example method for simultaneouslycommunicating with multiple communication devices in a WLAN, accordingto another embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) simultaneouslytransmits independent data streams to multiple client stations and/orreceives independent data streams simultaneously transmitted by multipleclient stations. In particular, the AP transmits data for the multipleclients in different orthogonal frequency division multiplexing (OFDM)sub-channel blocks of an orthogonal frequency division multiple access(OFDMA) transmission, in an embodiment. Similarly, multiple clientstations transmit data to the AP simultaneously, in particular, eachclient station transmits data in a different OFDM sub-channel block ofan OFDMA transmission, in an embodiment.

In an embodiment, the AP is configured obtain, for each client stationof a plurality of client stations, one or more quality indicatorscorresponding to one or more sub-channel blocks of an OFDM channelassociated with the client station. Based on the one or more qualityindicators of one or more sub-channel blocks received from each of oneor more client stations, the AP selects client stations to be includedin a group of client stations for OFDMA communication with the clientstations and/or allocates respective sub-channel blocks to clientstations in a group of client stations for OFDMA communication with theclient stations. The AP then communicates with the client stations in agroup of client station by simultaneously transmitting data to theclient stations in the respective sub-channel blocks allocated to theclient stations and/or receiving data simultaneously transmitted by theclient stations in the respective sub-channel blocks allocated to theclient stations, in an embodiment.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 includes differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 includesdifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. Two or more of the client stations 25are configured to receive corresponding data streams that aretransmitted simultaneously by the AP 14. Additionally, two or more ofthe client stations 25 are configured to transmit corresponding datastreams to the AP 14 such that the AP 14 receives the data streamssimultaneously.

A client station 25-1 includes a host processor 26 coupled to a networkinterface 27. The network interface 27 includes a MAC processing unit 28and a PHY processing unit 29. The PHY processing unit 29 includes aplurality of transceivers 30, and the transceivers 30 are coupled to aplurality of antennas 34. Although three transceivers 30 and threeantennas 34 are illustrated in FIG. 1, the client station 25-1 includesdifferent numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 30 andantennas 34 in other embodiments.

In an embodiment, one or more of the client stations 25-2, 25-3, and25-4 has a structure the same as or similar to the client station 25-1.In these embodiments, the client stations 25 structured like the clientstation 25-1 have the same or a different number of transceivers andantennas. For example, the client station 25-2 has only two transceiversand two antennas (not shown), according to an embodiment.

In an embodiment, the AP 14 is configured to transmit different OFDMunits to different client stations 25 simultaneously by forming an OFDMAdata unit that includes the different OFDM data units modulated inrespective sub-channel blocks of the OFDMA data unit. In an embodiment,the AP 14 allocates different sub-channels to different client stationsand forms the OFDMA data unit that includes OFDM data units directed toby modulating the different client stations in sub-channel blockscorresponding to the sub-channels assigned to the client stations.

FIGS. 2A, 2B, 2C and 2D are diagrams illustrating example OFDMsub-channel blocks for an 80 MHz communication channel, according to anembodiment. In FIG. 2A, the communication channel is partitioned intofour contiguous OFDM sub-channel blocks, each having a bandwidth of 20MHz. The OFDM sub-channel blocks include independent data streams forfour client stations. In FIG. 2B, the communication channel ispartitioned into two contiguous OFDM sub-channel blocks, each having abandwidth of 40 MHz. The OFDM sub-channel blocks include independentdata streams for two client stations. In FIG. 2C, the communicationchannel is partitioned into three contiguous OFDM sub-channel blocks.Two OFDM sub-channel blocks each have a bandwidth of 20 MHz. Theremaining OFDM sub-channel block has a bandwidth of 40 MHz. The OFDMsub-channel blocks include independent data streams for three clientstations. In FIG. 2D, the communication channel is partitioned into fourcontiguous OFDM sub-channel blocks. Two OFDM sub-channel blocks eachhave a bandwidth of 10 MHz, one OFDM sub-channel block has a bandwidthof 20 MHz, and one sub-channel block has a bandwidth of 40 MHz. The OFDMsub-channel blocks include independent data streams for three clientstations.

Although in FIGS. 2A, 2B, 2C, and 2D the OFDM sub-channel blocks arecontiguous across the communication channel, in other embodiments theOFDM sub-channel blocks are not contiguous across the communicationchannel (i.e., there are one or more gaps between the OFDM sub-channelblocks). In an embodiment, each gap is at least as wide as one of theOFDM sub-channel blocks. In another embodiment, at least one gap is lessthan the bandwidth of an OFDM sub-channel block. In another embodiment,at least one gap is at least as wide as 1 MHz. In an embodiment,different OFDM sub-channel blocks are transmitted in different channelsdefined by the IEEE 802.11a and/or 802.11n Standards. In one embodiment,the AP includes a plurality of radios and different OFDM sub-channelblocks are transmitted using different radios.

FIG. 3 is a diagram of an example OFDMA data unit 300, according to anembodiment. The OFDMA data unit 300 includes a plurality of OFDM dataunit 302-1, 302-2 and 302-3. In an embodiment, the AP 14 transmits theOFDM data units 302-1, 302-2, 302-3 to different client stations 25 viarespective OFDM sub-channels within the OFDMA data unit 300. In anotherembodiment, different client stations 25 transmit respective OFDM dataunits 302-1, 302-2, 302-3 to the AP 14 in respective OFDM sub-channelswithin the OFDMA data unit 300. In this embodiment, The AP 14 receivesthe OFDM data units 302-1, 302-2, 302-3 from the client stations 25 viarespective OFDM sub-channels of within the OFDMA data unit 300, in thisembodiment.

Each of the OFDM data units 302-1, 302-2, 302-3 conforms to acommunication protocol that supports OFDMA transmission, such as the HEWcommunication protocol, in an embodiment. In an embodiment in which theOFDMA data unit 300 corresponds to a downlink OFDMA data unit, the OFDMAdata unit 300 is generated by the AP 14 such that each OFDM data unit302 is transmitted to a respective client station 25 via a respectivesub-channel of the WLAN 10 allocated for downlink transmission of theOFDMA data unit 300 to the client station. Similarly, an embodiment inwhich the OFDMA data unit 300 corresponds to an uplink OFDMA data unit,the AP 14 receives the OFDM data units 302 via respective sub-channelsof the WLAN 10 allocated for uplink transmission of the OFDM data units302 from the client stations, in an embodiment. For example, the OFDMdata unit 302-1 is transmitted via a first 20 MHZ sub-channel of theWLAN 10, the OFDM data unit 302-2 is transmitted via a second 20 MHzsub-channel of the WLAN 10, and the OFDM data unit 302-3 is transmittedvia a 40 MHz sub-channel of the WLAN 10, in the illustrated embodiment.

In an embodiment, each of the OFDM data units 302 includes a preambleincluding one or more legacy short training fields (L-STF) 304, one ormore legacy long training fields (L-LTF) 306, one or more legacy signalfields (L-SIG) 308, one or more first high efficiency WLAN signal field(HEW-SIG-A) 310, N HEW long training fields (HEW-LTF) and a second HEWsignal field (HEW-SIGB) 314. Additionally, each OFDM data unit 302includes a high efficiency WLAN data portion (HEW-DATA) 318. In anembodiment, each L-LSF field 306, each L-LTF field 308, each L-SIG field310 and each HEW-SIGA field 312 occupies a smallest bandwidth supportedby the WLAN 10 (e.g., 20 MHz). In an embodiment, if an OFDM data unit302 occupies a bandwidth that is greater than the smallest bandwidth ofthe WLAN 10, then each L-LSF field 306, each L-LTF field 308, each L-SIGfield 310 and each HEW-SIGA field 312 is duplicated in each smallestbandwidth portion of the OFDM data unit 302 (e.g., in each 20 MHzportion of the data unit 302). On the other hand, each HEW-STF field312, each HEW-LTF field 314, each HEW-SIGB field 316 and each HEW dataportion 318 occupies an entire bandwidth of the corresponding OFDM dataunit 302, in an embodiment. For example, the OFDM data unit 302-3occupies 40 MHz, wherein L-LSF field 306, the L-LTF field 308, L-SIGfield 310 and HEW-SIGA fields 312 is duplicated in the upper and thelower 20 MHz bands of the OFDM data unit 302-3, while each of theHEW-STF field 312, each of the HEW-LTF fields 314, each of the HEW-SIGBfield 316 and each of the HEW data portion 318 occupies the entire 40MHz bandwidth of the data unit 302, in the illustrated embodiment.

In an embodiment, padding is used in one or more of the OFDM data units302 to equalize lengths of the OFDM data units 302. Accordingly, thelength of each of the OFDM data units 302 correspond to the length ofthe OFDMA data unit 302, in this embodiment. Ensuring that the OFDM dataunits 302 are of equal lengths synchronizes transmission ofacknowledgment frames by client stations 25 that receive the data units302, in an embodiment. In an embodiment, each of one or more of the OFDMdata units 302 is an aggregate MAC service data units (A-MPDU), which isin turn included in a PHY protocol data unit (PPDU). In an embodiment,padding (e.g., zero-padding) within one or more of the A-MPDUs 302 isused to equalize the lengths of the data units 302, and to synchronizetransmission of acknowledgement frames corresponding to the OFDMA dataunit 300.

In various embodiments, the AP 14 obtains, for each client station 25 ofa plurality of client stations 25, one or more quality indicatorscorresponding to one or more sub-channel blocks of the communicationchannel associated with the client station 25. Examples of qualityindicators that the AP 14 obtains include (i) a respective channelresponse indicator corresponding to each of one or more sub-channelblocks, (ii) a respective signal strength indicator corresponding toeach of one or more sub-channel blocks, (ii) a respective signal tonoise ratio (SNR) or signal to interference plus noise ratio (SNIR)indicator corresponding to each of one or more sub-channel blocks, (iv)an indicator corresponding to a “best” sub-channel block, (v) arespective indicator corresponding to order of preference of each of oneor more sub-channel blocks, etc., in various embodiments and/orscenarios. Then, based on the one or more quality indicators obtainedfor each client station 25 of the plurality of client stations 25, theAP 14 selects groups of client stations 25 for OFDMA communication withthe client stations 25 and/or allocates respective sub-channel blocks torespective client stations 25 in a group of client stations 25 selectedfor OFDMA communication with the client stations 25. The AP 14 thentransmits at least one OFDMA data unit to a group of client stations 25,wherein the OFDMA data unit includes respective OFDM data units directedto the client stations 25 of the group of client stations 25, in anembodiment. The respective OFDM data units are transmitted to the clientstations 25 in respective sub-channel blocks allocated to the clientstation 25, in an embodiment. Similarly, in an embodiment, the AP 14receives at least one OFDMA data unit from the group of client stations25, wherein the OFDMA data unit includes respective OFDM data unitstransmitted by the client stations 25 in respective sub-channel blocksallocated to the client station 25, in an embodiment. To this end, theAP 14 provides, in some manner, to a group of client stations 25indications of the respective sub-channel blocks allocated to the clientstations 25, in an embodiment.

In an embodiment, the AP 14 obtains the one or more quality indicatorscorresponding to one or more sub-channel blocks of a communicationchannel associated with a client station 25 based on sounding of thecommunication channel associated with the client station 25. Forexample, in an embodiment, the AP 14 explicitly sounds a communicationchannel associated a client station 25 by transmitting one or moretraining signals to the client stations 25 and, in response, receivingfeedback from the client station 25. The feedback includes the one ormore quality indicators corresponding to one or more sub-channel blocksof the communication channel, or includes indications of channelcharacteristics that allow the AP 14 to determine the one or morequality indicators, in various embodiments. In some embodiments, the AP14 obtains the one or more quality indicators corresponding to one ormore sub-channel blocks of a communication channel associated with aclient station 25 based on implicit sounding of the communicationchannel. In such embodiments, the AP 14 obtains channel characteristicsof a reverse channel from a client station 25 to the AP 14 based ontraining signal transmitted by the client station 25 to the AP 14. TheAP 14 then determines characteristics of the forward channel based onthe characteristics of the reverse channel by assuming channelreciprocity, and obtains the one or more quality indicatorscorresponding to one or more sub-channel blocks based on thecharacteristics of the forward channel, in some embodiments. To ensurechannel reciprocity, the AP 14 conducts a suitable calibration procedureto calibrate the receive and transmit radio frequency (RF) chains of theAP 14, in some embodiments. In some embodiments, the AP 14 obtains theone or more quality indicators corresponding to one or more sub-channelblocks directly based on characteristics of the reverse channel, withoutobtaining characteristics of the forward channel. For example, in anembodiment, the AP 14 obtains signal strength, signal to noise ratio,etc. associated with the one or more sub-channel blocks directly basedon the training signals received from the client station 25 in thereverse communication channel.

FIG. 4A is a timing diagram of an example sounding procedure 400 andtransmission of an example OFDMA data unit formed according to groupingand/or channel allocation determined based on the sounding procedure400, according to an embodiment. The sounding procedure 400 is anexplicit sounding procedure in which the AP 14 transmits a soundingpacket to each of a plurality of client stations 25 and receives, fromeach of the plurality client stations 25, feedback containing channelstate information and/or other indications corresponding to a forwardcommunication channel from the AP 14 to the client station 25.

During a time interval 402, the AP 14 transmits an announcement frame404 to a plurality of client stations 25 to initiate the soundingprocedure 400 with the client stations 25. The announcement frame 404identifies client stations 25 that are the intended participants in thesounding procedure 400, in an embodiment. The announcement frame 404 isa null data packet (NDP) that omits a payload, in an embodiment. Inanother embodiment, the announcement frame 404 includes a payload. In anembodiment, the announcement frame 404 identifies client stations 25 asintended participants in the sounding procedure 400 by including asuitable identifier, such as at least a portion of an associationidentifier (AID), corresponding to each of the client stations 25identified as an intended participant. In an embodiment, theannouncement frame 402 also indicates a length or a durationcorresponding to the sounding procedure 400, for example to protect thesounding procedure 400 from transmissions by communication devices thatare not intended participants in the sounding procedure 400. In anembodiment, each client station 25 identified by announcement frame 404determines, based on detecting its own AID in the announcement frame404, that the client station 25 is an intended participant in thesounding procedure 400. In the event that the management frame 404 doesnot include the AID of a particular client station 25, that clientstation 25 determines that it is not an intended participant in thesounding procedure 400 and refrains from accessing the channel for theduration indicated by the announcement frame 404, in an embodiment.

During a time interval 406, the AP 14 transmits a sounding frame 408that includes one or more training signals that allow each clientstation 25 to obtain a measure of the forward communication channel fromthe AP 14 to the client station 25. In an embodiment, the sounding frame404 is a null data packet that includes the one or more training signalsin a PHY preamble of the data unit, and omits a payload. In anotherembodiment, the sounding frame 404 includes a PHY preamble and a payloadportion. In an embodiment, each of the client station 25 identified bythe announcement frame 408 obtains, based on training informationincluded in the sounding frame 408, a channel description characterizingthe communication channel between the AP 14 and the client station 25and/or quality of one or more of the sub-channel blocks of thecommunication channel between the AP 14 and the client station 25. Forexample, each client station 25 obtains channel state information (e.g.,the gain, the phase, the signal to noise ratio (SNR), etc.)characterizing the communication channel between the AP 14 and theclient station 25 over the entire bandwidth of the communicationchannel, in an embodiment. Additionally or alternatively, in anembodiment, each client station 25 determines channel quality indicators(e.g., SNR, SNIR, signal strength, etc.) corresponding to eachsub-channel block of the communication channel between the AP 14 and theclient station 25. In some embodiments, each client station 25identifies one or more preferred sub-channel blocks for the clientstation 25, and determines an order of preference of the identifiedpreferred sub-channel blocks.

During a time intervals 410, the client stations 25 transmit respectivefeedback packets 414 to the AP 14. In an embodiment, a feedback packet414 from a particular client station 25 includes one or more of (i)indications of one or more preferred sub-channel blocks identified bythe particular station 25, (ii) indications of order of preference ofmultiple preferred sub-channel blocks identified by the particularstation 25 (iii) one or more channel quality indicators, such as channelstate information (CSI) or other suitable channel characteristics,corresponding to each of one or more sub-channel blocks of thecommunication channel between the AP 14 and the particular clientstation 25, (iv) CSI or other suitable channel description correspondingto the entire bandwidth of the communication channel between the AP 14and the particular client station 25, such as CSI corresponding to eachsub-carrier or CSI corresponding to each group of sub-carriers of thecommunication channel between the AP 14 and the particular clientstation 25 (v) SNR corresponding to the entire bandwidth of thecommunication channel between the AP 14 and the particular clientstation 25, etc.

In an embodiment, a client station 25 (e.g., the client stations 25-1)identified first in the announcement frame 402 transits its feedbackpacket 412-1 during a time interval that begins upon expiration of acertain predetermined time interval, such as a time intervalcorresponding to SIFS or another suitable predetermined time interval,after completion of reception of the sounding packet 404 by the clientstation 25. The AP 14 receives the feedback packet 412-1 from the firstclient station 25 and successively polls for feedback from each of theremaining client stations 25 identified by the announcement frame 404 asparticipants in the sounding procedure 400, in an embodiment. Forexample, the AP successively transmits respective immediate responserequest (IRR) frames 414 to each of the remaining client stations 25identified by the announcement frame 404 as participants in the soundingprocedure 400, in an embodiment. Each of the remaining client stations25 transmits its feedback packet 412 during a time interval that beginsupon expiration of a certain predetermined time interval, such as a timeinterval corresponding to SIFS or another suitable time interval, aftercompletion of reception by the client station 25 the IRR frame 414directed to the client station 25, in an embodiment.

Based on the feedback packets 412 received by the AP 14 during the timeinterval 410, the AP 14 obtains one or more quality indicatorscorresponding to one or more sub-channel blocks of the communicationchannel between the AP 14 and each of the client stations 25 thatparticipated in the sounding procedure 400, in an embodiment. Forexample, the AP 14 obtains the one more quality indicators for aparticular client station 25 directly from the feedback packet 414received from the particular client station 25, in an embodiment. Inanother embodiment, the AP 14 determines the one or more qualityindicators for a particular client station 25 based on data included inthe feedback packet 412 received from the client station 25, such asbased on CSI or other channel description included in the feedbackpacket 412 received from the client station 25. During a time interval416, based on the quality indicators obtained for at least some of theclient stations 25, the AP 14 selects one or more groups of clientstations 25 for OFDMA communication with the client statins 25 and/orallocates respective sub-channel blocks to client stations 25 selectedas members of a group of client stations 25 for OFDMA communication withthe client statins 25, in an embodiment. During a time interval 418, theAP 14 transmits an OFDMA data unit 420 to a group of client stations 25selected as members of a group of client stations 25 for OFDMAcommunication with the client statins 25, in an embodiment. The OFDMAdata unit 420 includes respective OFDM data units directed to the clientstations 25 of the group, wherein the respective OFDM data units aretransmitted to the client statins 25 in the respective sub-channelblocks allocated to the client stations 25, in an embodiment.

With continues reference to FIG. 4A, in some embodiments, soundingprocedure 400 is used for the purpose of beamforming as well as OFDMAcommunication. For example, in addition to generating feedback relatedto quality of sub-channel blocks for OFDMA communication, each clientstation 25 develops, based on the training signals in the soundingpacket 408, beamforming feedback, and provides the beamforming feedbackto the AP 14. For example, each feedback packet 412 includes beamformingfeedback in addition to the feedback related to OFDMA communication, inan embodiment. FIG. 4B is a diagram of a feedback packet 450 that aclient station 25 is configured to transmit to the AP 14 during thesounding procedure 400 of FIG. 4A, according to one such embodiment. Inan embodiment, the feedback packet 450 corresponds to each of thefeedback packets 412 of FIG. 4A. In an embodiment, the feedback packet450 is generated by a client station 25 in response to receiving asounding packet transmitted by the AP 14 to the client station 25. Forexample, the PHY processing unit 29 of the client station 25-1 isconfigured to generate feedback packets such as the feedback packet 450,in an embodiment.

The feedback packet 450 includes a MIMO control field 452, a beamformingfeedback portion 454 and an OFDMA feedback portion 456. The beamformingfeedback portion 452 includes an average SNR subfield 458, a beamformingfeedback sub-field 460 and a per-tone SNR sub-field 462. The beamformingfeedback sub-field 460 includes some form of beamforming feedbackgenerated at the client station 25 based on a sounding packettransmitted by the AP 14 to the client station 25, in variousembodiments. For example, in an embodiment, the beamforming feedbacksub-field 460 includes compressed steering feedback. For example, thebeamforming feedback sub-field 460 includes compressed steering feedbackfor multi-user (MU) multiple input multiple output (MIMO) as defined inthe IEEE 802.11 ac standard. In another embodiment, the beamformingfeedback sub-field 460 includes another suitable form of beamformingfeedback, such as channel estimate feedback or uncompressed steeringmatrix feedback, for example. In an embodiment, each of the average SNRsubfield 458, the beamforming feedback sub-field 460 and the per-toneSNR sub-field 462 includes feedback that covers the entire bandwidth ofthe communication channel. In an embodiment, each of the average SNRsubfield 458, the beamforming feedback sub-field 460 and the per-toneSNR sub-field 462 includes feedback that covers the bandwidth of thesounding packet based on which the beamforming feedback was generated bythe client station 25.

The OFDMA feedback portion 456 includes OFDMA feedback as describedabove with respect to FIG. 4A, in an embodiment. For example, the OFDMAportion 456 includes one or more of (i) indications of one or morepreferred sub-channel blocks identified by the client station 25 basedon the sounding frame transmitted by the AP 14 to the client station 25,(ii) indications of order of preference of multiple preferredsub-channel blocks identified by the particular station 25 based on thesounding frame based on the sounding frame transmitted by the AP 14 tothe client station 25 (iii) one or more channel quality indicators, suchas CSI or other suitable channel quality indicators, corresponding toeach of one or more sub-channel blocks of the communication channelbetween the AP 14 and the client station 25, (iv) CSI corresponding tothe entire bandwidth of the communication channel between the AP 14 andthe client station 25, such as CSI corresponding to each sub-carrier orCSI corresponding to each group of sub-carriers of the communicationchannel between the AP 14 and the client station 25, and (v) SNRcorresponding to the entire bandwidth of the communication channelbetween the AP 14 and the particular client station 25.

In an embodiment, the feedback packet 450 omits one or more of theaverage SNR subfield 458, the beamforming feedback sub-field 460 and theper-tone SNR sub-field 460. In an embodiment, the feedback packet 450omits the entire beamforming feedback portion 452. For example, thefeedback packet 450 omits the entire beamforming feedback portion 452 inan embodiment in which the AP 14 includes a single transmit antennaand/or if the AP 14 is not configured to perform beamforming or is notconfigured to perform multi-user beamforming.

In some embodiments, at least a portion of OFDMA feedback is included inthe MIMO control field 452 of the feedback packet 540. For example,indications of one or more preferred sub-channel blocks are included inthe MIMO control field 452. In some such embodiments, the feedbackpacket 450 omits the OFDMA feedback portion 454.

FIG. 4C is a diagram of a feedback packet 470 that a client station 25is configured to transmit to the AP 14 during the sounding procedure 400of FIG. 4A, according to another embodiment. In an embodiment, thefeedback packet 470 corresponds to a feedback packet 412 of FIG. 4A. Thefeedback packet 470 is generally the same as the feedback packet 450,except that a beamforming portion 470 includes a beamforming feedbackportion 474 that covers a bandwidth that corresponds to the one or moresub-channel blocks indicated by the OFDMA feedback portion 456.

FIG. 5 is a timing diagram of an example sounding procedure 500 andtransmission of an example OFDMA data unit formed according to groupingand/or channel allocation determined based the sounding procedure 500,according to an embodiment. The sounding procedure 500 is an implicitsounding procedure in which the AP 14 requests transmission of one ormore training signals from each client station 25 of a plurality ofclient stations 25. The AP 14 receives the requested one or moretraining signals from each of the plurality of client stations 25, andobtains, for each of the client stations 25, one or more qualityindicators corresponding to one or more sub-channel blocks of thecommunication channel associated with the client station 25, in anembodiment.

Referring to FIG. 5, during a time interval 502, the AP 14 sequentiallytransmits respective control frames 504 to each of a plurality of clientstations 25. Each control frame 504 is directed to a particular clientstation 25 and includes a request for transmission of one or moretraining signals by the client station 25. In response to receiving therespective control frames 504, the client stations 25 transmitrespective sounding frames 506 to the AP 14. Each sounding frame 506includes one or more training signals, in an embodiment. For example,each sounding frame 504 includes one or more training fields in apreamble portion of the sounding frame 504. In an embodiment, eachsounding frame 504 is an NDP that omits a payload. In anotherembodiment, each sounding frame 504 includes a payload. Each clientstation 25 transmits its sounding frame 506 upon expiration of a certainpredetermined time period, such as a time period corresponding to SIFSor another predetermined time period, after completion of reception ofthe corresponding control frame 504 by the client station 25, in anembodiment.

The AP 14 receives a sounding frame 504 from a client station 25 andobtains, based on the sounding frame 504, one or more quality indicatorscorresponding to one or more sub-channel blocks of the communicationchannel between the AP and the client station 25. For example, the AP 14obtains, based on the sounding packet 504, an estimate of the reversecommunication channel from the client station 25 to the AP 14, in anembodiment. The estimate of the reverse channel can be represented, forexample, in a matrix format as a two-dimensional channel matrix H thatspecifies, in each element, a channel gain parameter for a spatialstream defined by a transmit antenna of the client station 25 and areceive antenna of the AP 14. In an embodiment, the AP 14 determines anestimate of the forward communication channel from the AP 14 to theclient station 25 based on the reverse communication channel from theclient station by assuming channel reciprocity. For example, the AP 14obtains an estimate of the forward channel by transposing the channelmatrix H obtained for the reverse channel. The AP 14 then obtainsrespective quality indicators corresponding to one or more sub-channelblocks of the commination channel based on the forward channel estimatecorresponding to the channel. In an embodiment the AP 14 obtains areverse and forward channel estimate corresponding to each OFDM tone ofthe communication channel or a subset of OFDM tones, such as each secondOFDM tone, each 4^(th) OFDM tone, or any other suitable subset of OFDMtones of the communication channel. The AP 14 then obtains the qualityindicators corresponding to each sub-channel blocks of the communicationchannel based on channel estimates corresponding to OFDM tones includedin the sub-channel block, in an embodiment.

In another embodiment, the AP 14 obtains, from training data included inthe sounding packet 504, a measure indicative of quality of the reversecommunication channel, such a measure of signal strength, signal tonoise ratio, etc. associated with the communication channel. In anembodiment, the AP 14 obtains such measure for each sub-carrier or eachgroup of sub-carriers of the communication channel, and obtains thechannel quality indicators corresponding to one or more sub-channelblocks based on the measure of the reverse communication channel. In anembodiment, the AP 14 selects one or more “best” or “preferred”sub-channel blocks for each of the stations 25. In an embodiment, the AP14 ranks one or more sub-channel blocks in order of preference for eachof the client stations 25. Examples of quality indicators that the AP 14obtains for one or more sub-channel blocks include one or more of (i) arespective channel response indicator corresponding to each of one ormore sub-channel blocks, (ii) a respective signal strength indicatorcorresponding to each of one or more channel blocks, (ii) a respectiveSNR or SNIR indicator corresponding to each of one or more sub-channelblocks, (iv) an indicator corresponding to a “best” sub-channel block,(v) a respective indicator corresponding to order of preference of eachof one or more sub-channel blocks.

During a time interval 508, based on the quality indicators obtainedbased on the sounding procedure 500, the AP 14 selects one or moregroups of client stations 25 for OFDMA communication with the clientstatins 25 and/or allocates respective sub-channel blocks to clientstations 25 selected as members of a group of client stations 25 forOFDMA communication with the client statins 25. During a time interval510, the AP 14 transmits an OFDMA data unit 512 to a group of clientstations 25 selected as members of a group of client stations 25 forOFDMA communication with the client statins 25. The OFDMA data unit 512includes respective OFDM data units directed to the client stations 25of the group, wherein the respective OFDM data units are transmitted tothe client statins 25 in the respective sub-channel blocks allocated tothe client stations 25, in an embodiment.

In some embodiments, the implicit sounding procedure 500 is conducted bythe AP 14 for the purpose of beamforming as well as for OFDMA groupselection and/or sub-channel block allocation. For example, the AP 14 isconfigured to determine a transmit beamsteering matrix for use intransmitting to one or more client stations 25 based on the soundingpackets 506 received from the one or more client stations 25, in anembodiment.

FIG. 6 is a timing diagram of an example sounding procedure 600 andtransmission of an example OFDMA data unit formed according to groupingand/or channel allocation determined based the sounding procedure 600,according to an embodiment. The sounding procedure 600 is a transparentimplicit sounding procedure in which the AP 14 obtains one or morequality indicators corresponding to one or more sub-channel blocks of acommunication channel associated with a client station 25 based on oneor more “regular” data units received from the client station 25.

In an embodiment, during a time interval 602, the AP 14 receives aplurality of regular data units 604 from a plurality of client stations25. Each regular data unit 604 includes one or more training signals(e.g. in a preamble portion of the regular data unit) that allow the AP14 at least practically characterize the reverse channel from acorresponding client station 25 to the AP 14.

As used herein, a regular data unit is a non-sounding data unit used inany procedure other than channel sounding, e.g., data exchange,modulation and coding scheme (MCS) feedback, etc. In an embodiment, eachregular data unit 604 is a communication frame, a data packet, etc. Inan embodiment, the regular data units 604 are generally not soundingphysical layer convergence procedure (PLCP) protocol data unit (PPDU) ornull data packets (NDP) used specifically for sounding. In someembodiments, the regular data units 604 do not include respectiveindications that the data units 604 are for sounding a communicationchannel (while data units used for sounding communication channelsinclude such an indication). Further, in some embodiments, the regulardata units 604 include explicit respective indications that the dataunits 604 are not for sounding the communication channel. Still further,in some embodiments, the regular data units 604 are not transmitted inresponse to a request to transmit a sounding packet. A client stations25 transmits a regular data unit 604 for a purpose unrelated to soundingthe communication channel. For example, in an embodiment, a regular dataunit 604 is a data packet that includes a data payload. The implicitchannel sounding procedure is therefore transparent to the clientstations 25.

In some embodiments, a client station 25 transmits a data unit 604 usingmultiple spatial streams, and the data unit 604 accordingly includesinformation (e.g., training fields in the physical layer (PHY) preamble)that can be used to obtain channel characteristics of the reversechannel from the client station 25 to the AP 14. For example, the dataunit 604 can include a payload transmitted over three spatial streamsand, accordingly, three training fields in the PHY preamble to enablethe AP 14 to properly process the payload.

In an embodiment, the AP 14 obtains, based on training informationincluded in the regular data unit 604, channel state information (CSI)that describes one or more characteristics of each spatial streamassociated with the reverse channel (e.g., gain, phase, SNR, etc.). TheCSI can be represented, for example, in a matrix format as atwo-dimensional channel matrix H that specifies, in each element, achannel gain parameter for a spatial stream defined by the correspondingtransmit antenna and a receive antenna. To generate an estimate of theforward channel, in an embodiment, the AP 14 calculates the transpose ofthe matrix that describes the reverse channel. In doing so, the AP 14assumes that the MIMO channel between the AP 14 and the client station25 is symmetrical so that the forward channel and the reverse channelcan be considered to be reciprocal.

In some embodiments, a regular data unit 604 received from a clientstation 25 in some cases includes fewer training fields than spatialdimensions associated with the communication channel associated with theclient station 25. In an embodiment, the AP 14 obtains a measurepartially characterizing the communication channel, and obtains the oneor more quality indicators corresponding to one or more sub-channelblocks of the communication channel based on the measure partiallycharacterizing the communication channel. In some embodiment, the AP 14does not use every regular data unit received from a client station 25to obtain characteristics of the communication channel between the AP 14and the client station 24. For example, the AP 14 selects regular dataunits based on which to obtain characteristics of the communicationchannel according to one or more suitable selection criteria. Forexample, the AP 14 selects regular data units transmitted by a clientstation 25 using all spatial dimensions associated with thecommunication channel between the AP 14 and the client station 25, in anembodiment.

In an embodiment the AP 14 obtains, based on one or more data units 604,characteristics of a communication channel corresponding to each OFDMtone of the communication channel or a subset of OFDM tones, such aseach second OFDM tone, each 4^(th) OFDM tone, or any other suitablesubset of OFDM tones of the communication channel. The AP 14 thenobtains the quality indicators corresponding to each sub-channel blocksof the communication channel based on channel estimates corresponding toOFDM tones included in the sub-channel block, in an embodiment.

During a time interval 606, based on the quality indicators obtainedbased on the sounding procedure 600, the AP 14 selects one or moregroups of client stations 25 for OFDMA communication with the clientstatins 25 and/or allocates respective sub-channel blocks to clientstations 25 selected as members of a group of client stations 25 forOFDMA communication with the client statins 25. During a time interval608, the AP 14 transmits an OFDMA data unit 610 to a group of clientstations 25. The OFDMA data unit 610 includes respective OFDM data unitsdirected to the client stations 25 of the group, wherein the respectiveOFDM data units are transmitted to the client statins 25 in therespective sub-channel blocks allocated to the client stations 25, in anembodiment.

In some embodiments, the transparent implicit sounding procedure 600 isconducted by the AP 14 for the purpose of beamforming as well as forOFDMA group selection and/or sub-channel block allocation. For example,the AP 14 is configured to determine a transmit beamsteering matrix foruse in transmitting to one or more client stations 25 based on trainingdata included on the data units 604 received from the client stations25, in an embodiment.

In various embodiments, prior to transmitting an OFDMA data unit to agroup of client stations 25, the AP 14 informs, or notifies, the clientstations 25 that the client stations 25 are members of a group of clientstations 25 for OFDMA communication with the client stations 25. FIG. 7is a timing diagram illustrating a notification procedure 700 used bythe AP 14 to inform a plurality of client stations 25 that the clientstations 25 are members of a group of client stations 25 for OFDMAcommunication, according to an embodiment. The AP 14 transmits a groupmanagement frame 702 to a plurality of client stations 25. The groupmanagement frame 702 informs the plurality of client statins 25 that theclient stations 25 are members of a group for OFDMA communication withthe client stations 25. In an embodiment, the group management frame 702includes a group number field and a plurality of station identificationfields. Each station identification field includes an identifier, suchas, for example, an association identifier (AID) or a partial AID,associated with a particular client station 25. Each client station 25that receives the group management frame determines whether that clientstation 25 is a member of the group identified by the group numberindicated in the group management frame 702, in an embodiment. Forexample, a client station 25 that receives the group management frame704 determines that the client station 25 is a member of the groupindicated by the management frame 702 by detecting its own AID orpartial AID in one of the station identification field included in themanagement frame 702. In an embodiment, the client station 25 furtherdetermines its position within the group based on placement of its AIDrelative to placement of the other AIDS within the management frame 702.

During a time interval 704, the client stations 25 identified by thegroup management group 702 transmit respective acknowledgement frame 706to the AP 14. In an embodiment, the client station 25 identified firstin the group management frame 702 transits its acknowledgement frame706-1 during a time interval that begins upon expiration of a certainpredetermined time interval, such as a time interval corresponding toSIFS or another suitable predetermined time interval, after completionof reception of the group management frame 704 by the client station 25.The AP 14 receives the acknowledgement frame 706-1 from the first clientstation 25 and successively polls for acknowledgement frames from eachof the remaining client stations 25 identified by the group managementframe 704, in an embodiment. For example, the AP 14 successivelytransmits respective poll frames 708 to each of the remaining clientstations 25 of the group of client stations 25. Each of the remainingclient stations 25 transmits its acknowledgement frame 706 during a timeinterval that begins upon expiration of a certain predetermined timeinterval, such as a time interval corresponding to SIFS or anothersuitable time interval, after completion of reception by the clientstation 25 of the poll frame 708 directed to the client station 25, inan embodiment. After receiving the respective acknowledgement frames 708from the client stations 25, the AP 14 transmits one or more OFDMA dataunits to the group of client stations 25, in an embodiment. To indicateto the client stations that an OFDMA data unit is directed to the groupof client stations, the AP 14 includes, in the OFDMA data, the group IDprovided to the client stations 25 by the group management frame 802, inan embodiment.

FIG. 8 is a timing diagram illustrating a notification procedure 800used by the AP 14 to inform a plurality of client stations 25 that theclient stations 25 are members of a group of client stations for OFDMAcommunication, according to another embodiment. The procedure 800 issimilar to the procedure 700 of FIG. 7, except that in the notificationprocedure 800, the AP 14 transits a respective group announcement frame802 to each client station 25 included in the group. In an embodiment,each management frame 802 is substantially the same as the groupmanagement frame 702 of FIG. 7. In an embodiment, a client station 25that receives the group management frame 802 directed to the group ofclient stations 25 determines that the client station 25 belongs to thegroup of client stations 25 based on its own AID in the group managementframe 802. In an embodiment, the client station 25 further determinesits position within the group based on placement of its AID relative toplacement of the other AIDs within the management frame 802. Afterreceiving management frame 802 directed to a client station 25, theclient station 25 transmits an acknowledgement frame 804 to the AP 14.In an embodiment, each client station 25 transmits an acknowledgmentframe 804 during a time interval that begins upon expiration of acertain predetermined time interval, such as a time intervalcorresponding to SIFS or another suitable time interval, aftercompletion of reception by the client station 25 of the group managementframe 802 directed to the client station 25, in an embodiment. Afterreceiving the respective acknowledgement frames 804 from the clientstations 25, the AP 14 transmits one or more OFDMA data units to thegroup of client stations 25, in an embodiment.

In various embodiments, the AP 14 employs static allocation, semi-staticallocation or dynamic allocation to allocate respective sub-channelblocks to client stations 25 in a group for OFDMA communication with theclient station 25. In an embodiment in which the AP 14 employs staticallocation, the AP 14 allocates respective sub-channel blocks to clientstations 25 in a group of client stations 25 for OFDMA communicationwith the client station 25 when the AP 14 forms the group, of clientstations 25, and the sub-channel block allocation to the client stations25 persists for the life of the group. In an embodiment, the AP 14indicates to the client stations 25 that belong to a group using a groupmanagement frame that notifies the client stations 25 of theirmembership in the group. For example, the group management frame 702 ofFIG. 7 identifies a group of client stations 25, and also includesindications of respective sub-channel blocks allocated to each of theidentified client stations 25. Similarly, each group management frame802 of FIG. 8 includes indications of respective sub-channel blocksallocated to each of the identified client stations 25 identified by thegroup management frame 802, in an embodiment.

In an embodiment in which the AP 14 employs semi-static sub-channelblock allocation, allocation of the sub-channel blocks to clientstations 25 in a group can change during the life of the group. Forexample, the AP 14 periodically obtains, for each of the client stations25 in a group, one or more quality indicators corresponding to one ormore sub-channel blocks of the channel associated with the clientstations 25 in the group, and determines a suitable sub-channel blockallocation to the client stations of the group each time new qualityindicators are obtained for the client stations 25 in the group. Forexample, the AP 14 utilizes the sounding procedure 400 of FIG. 4A, thesounding procedure 500 of FIG. 5, the sounding procedure 500 of FIG. 6,or another suitable channel sounding procedure to periodically obtainquality indicators corresponding to one or more sub-channel blocks ofthe channel associated with the client stations 25 in the group, andperforms sub-channel block allocation based on quality indicatorsobtained based on the sounding procedure. In an embodiment, the APtransmits one or more group management frames to the client stations 25in a group to inform the client stations 25 of new sub-channel blocksallocated to the client stations 25 each time the AP 14 completes asounding procedure and allocates sub-channel blocks allocated to theclient stations 25 based on the sounding procedure.

In an embodiment in which the AP 14 employs dynamic sub-channel blockallocation, the AP 14 allocates sub-channel blocks to client station 25in a group on packet-per-packet basis, for example prior to transmissionof each OFDMA data unit to the client stations of the group. In anembodiment in which the AP 14 employs dynamic sub-channel blockallocation the AP 14 indicates to the client statins 25 in a group thesub-channel blocks allocated to the client stations 25 for a particularOFDMA transmission to the client stations 25 by including theindications in a preamble of the OFDMA transmission. For example, in anembodiment, the sub-channel block allocation indications are included ina signal field of the OFDMA transmission. With reference to FIG. 3, thesub-channel block allocation indications are included in the HEW-SIGAfields 310, in an example embodiment. In an embodiment, the signal fieldof the OFDMA transmission includes a group number subfield thatidentifies a group of client stations 25, and respective sub-channelallocation subfields corresponding to the client stations 25 of theidentified group. In an embodiment, the sub-channel allocation subfieldsin the signal field are provided in the order corresponding to clientstation position within the group, wherein the client station positioncorresponds to the client station position determined by each clientstation 25 based on a group management frame previously received by theclient station 25. When receiving an OFDMA transmission directed to agroup of client stations 25, each client station 25 that is a member ofthe group determines, based on the sub-channel allocation subfieldcorresponding to the client station 25 in the signal field of the OFDMAtransmission, which sub-channel block within the OFDM transmission isallocated to the client station 25, in an embodiment.

In some embodiments, client stations 25, rather than AP 14, conductchannel sounding to obtain one or more quality indicators correspondingto one or more sub-channel blocks of the communication channelassociated with the client stations 25, and provide indications of oneor more preferred sub-channel blocks to the AP 14. In an embodiment, theclient stations 25 conduct explicit channel sounding similar to thesounding procedure 400 described above with respect to FIG. 4A, andobtain characteristics of the communication channels between the AP 14and the client stations 25 based on explicitly sounding thecommunication channels. For example, a client station 25 initiates asounding procedure with AP 14 by transmitting a sounding packet the sameas or similar to the sounding packet 408 to the AP 14. The AP 14provides feedback to the client station 25, such as via a feedbackpacket the same as or similar to one of the feedback packets 412. Theclient station 25 obtains one or more quality indicators correspondingto one or more sub-channel blocks of the communication channel based onthe feedback received from the AP 14, and identifies one or moresub-channel blocks preferred by the client station 25 to be used forOFDMA communication with client station 25. In an embodiment, the clientstation 25 identifies multiple sub-channel blocks preferred by theclient station 25 to be used for OFDMA communication with the clientstation 25, and ranks the multiple sub-channel blocks in order ofpreference. The client station 25 then provides indications of the oneor more preferred sub-channel blocks, and, if determined, indications ofthe order of preference of the sub-channel blocks, to the AP 14.

In another embodiment, a client station 25 conducts an implicit channelsounding procedure with the AP 14, similar to the sounding procedure 500described above with respect to FIG. 5, and obtains quality indicationscorresponding to one or more sub-channel blocks of the communicationchannel based on the implicit sounding procedure. For example, theclient station 25 transmits a request to the AP 14 requesting trainingsignals to be transmitted by the AP 14. In response to the request, theAP 14 transmits a sounding packet to the client station 25. The clientstation 25 obtains characteristics of the communication channel based onthe received sounding frame, selects one or more preferred sub-channelblocks, and, in some embodiments, ranks selected multiple sub-channelblocks in order of preference. The client station 25 then providesindications of the one or more selected sub-channel blocks and, ifdetermined, rankings corresponding to order of preference of the one ormore sub-channel blocks to the AP 14. Similarly, in an embodiment, aclient station 25 conducts a transparent implicit sounding procedure,similar to the transparent implicit sounding procedure 600 describedabove with respect to FIG. 6. For example, the client station 25 obtainscharacteristics of the channel between the client station 25 and the AP14 based on one or more regular data units received from the AP 14,selects one or more preferred sub-channel blocks based on thetransparent implicit sounding procedure, and provides indications of theone or more preferred sub-channel blocks, and, in some embodiments,indications of the order of preference of the sub-channel blocks, to theAP 14.

The AP 14 obtains respective indications of preferred sub-channel blocksand/or indications of order of preference of the sub-channel blocks,from each of a plurality of client stations 25. Based on the respectiveindications obtained from the plurality of client stations 25, the AP 14selects a group of client stations 25 for OFDMA communication and/orallocates respective sub-channel blocks to respective client stations 25that are members of a group for OFDMA communication, in variousembodiments.

FIG. 9 is a flow diagram of an example method 900 for simultaneouslycommunicating with multiple communication devices in a WLAN, accordingto an embodiment. In an embodiment, the method 900 is implemented by anAP in the WLAN, according to an embodiment. With reference to FIG. 1,the method 900 is implemented by the AP 14. For example, the method 900is implemented by the MAC processing unit 18 and/or by the PHYprocessing unit 20 of the AP 14, in an embodiment. In other embodiments,the method 900 is implemented by other components of the AP 14, or isimplemented by a suitable communication device other than the AP 14.

At block 902, one or more quality indicators are obtained for eachclient station of a plurality of client stations. The one or morequality indicators obtained for a client station correspond torespective one more such channel blocks of an OFDM communication channelassociated with the client station. At block 904, a group of clientstations for OFDMA communication is selected based on the qualityindicators obtained for at least some of the client stations at block902. At block 906 an OFDMA data unit is transmitted to the group ofclient stations selected at block 902. Each of the OFDMA data unitsincludes respective OFDM data units transmitted to the client stationsof the group. The respective OFDM data units are transmitted to thecommunication devices in respective sub-channel blocks allocated to thecommunication devices.

FIG. 10 is a flow diagram of an example method 100 for simultaneouslycommunicating with multiple communication devices in a WLAN, accordingto an embodiment. In an embodiment, the method 1000 is implemented by anAP in the WLAN, according to an embodiment. With reference to FIG. 1,the method 900 is implemented by the AP 14. For example, the method 1000is implemented by the MAC processing unit 18 and/or by the PHYprocessing unit 20 of the AP 14, in an embodiment. In other embodiments,the method 1000 is implemented by other components of the AP 14, or isimplemented by a suitable communication device other than the AP 14.

At block 1002, one or more quality indicators are obtained for eachclient station in a group of client stations for OFDMA communication.The one or more quality indicators obtained for a client stationcorrespond to respective one more such channel blocks of an OFDMcommunication channel associated with the client station. At block 1004,respective sub-channel blocks are allocated to the two or more clientstations of the group. The respective sub-channel blocks are allocatedbased on the quality indicators obtained at block 1002 for at least someof the two or more client stations of the group. At block 1006, an OFDMAdata unit is transmitted to the group of client stations. Each of theOFDMA data units includes respective OFDM data units transmitted to theclient stations of the group. The respective OFDM data units aretransmitted to the client stations in respective sub-channel blocksallocated to the client stations at block 1004.

In an embodiment, a method for simultaneously communicating withmultiple communication devices in a communication network includesobtaining, at a first communication device for each second communicationdevice of a plurality of second communication devices, one or morequality indicators corresponding to one or more sub-channel blocks of anorthogonal frequency division multiplexing (OFDM) communication channelassociated with the second communication device. The method alsoincludes selecting, at the first communication device based on thequality indicators obtained for each of at least some of the secondcommunication devices, a group of second communication devices fororthogonal frequency division multiple access (OFDMA) communication,wherein the group includes two or more second communication devices ofthe plurality of second communication devices. The method additionallyincludes transmitting, from the first communication device to the groupof second communication devices, at least one OFDMA data unit thatincludes respective OFDM data units directed to the two or more secondcommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more second communication devices of the group.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

Obtaining, at the first communication device for each secondcommunication device of the plurality of second communication devices,one or more quality indicators corresponding to one or more sub-channelblocks of OFDM communication channel associated with the secondcommunication device comprises transmitting a sounding packet from thefirst communication device to the plurality of second communicationdevices, receiving, at the first communication device, a plurality ofrespective feedback packets from the plurality of second communicationdevices, wherein the feedback packets include feedback generated basedon the sounding packet, and obtaining the one or more quality indicatorsfor each second communication device based on the feedback packetreceived from the second communication device.

Obtaining, at the first communication device for each secondcommunication device of the plurality of second communication devices,one or more quality indicators corresponding to one or more sub-channelblocks of the OFDM communication channel associated with the secondcommunication device comprises transmitting a request frame from thefirst communication device to the plurality of second communicationdevices, wherein the request frame requests the second communicationdevices to transmit respective sounding frames to the firstcommunication device, receiving, at the first communication device,respective sounding packets transmitted by the second communicationdevices in response to the requests frame, and obtaining the one or morequality indicators for each second communication device based on thesounding packet received from the second communication device.

Obtaining, at the first communication device for each secondcommunication device of the plurality of second communication devices,one or more quality indicators corresponding to one or more sub-channelblocks of the OFDM communication channel associated with the secondcommunication device comprises receiving, at the first communicationdevice, respective non-sounding data units transmitted by the secondcommunication devices for purposes other than sounding the OFDMcommunication channels associated with the second communication devices,and obtaining the one or more quality indicators for each secondcommunication device based on the non-sounding packet received from thesecond communication device.

Obtaining, at the first communication device for each secondcommunication device of the plurality of second communication devices,one or more quality indicators corresponding to one or more sub-channelblocks of the OFDM communication channel associated with the secondcommunication device comprises obtaining, for each second communicationdevice one or both of (i) indications of one or more preferredsub-channel blocks for the second communication device and (ii)indications of order of preference of multiple preferred sub-channelblocks for the second communication device.

The method further includes, prior to transmitting the at least oneOFDMA data unit to the group of second communication devices,transmitting a group management frame to indicate to the secondcommunication devices of the group that the second communication devicesare members of the group.

The method further includes allocating, based on the quality indicatorsobtained for the two or more second communication devices of the group,the respective sub-channel blocks to the two or more secondcommunication devices of the group.

The method further includes after transmitting the at least one OFDMAdata unit to the group of second communication devices, obtaining, foreach of the second communication devices of the group, one or more newquality indicators corresponding to one or more sub-channel blocks ofthe OFDM communication channel associated with the second communicationdevice, allocating respective sub-channel blocks to the secondcommunication devices of the group based on the new quality indicators,and transmitting at least one additional OFDMA data unit that includesrespective OFDM data units directed to the two or more secondcommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more second communication devices based on the new qualityindicators.

In another embodiment, an apparatus for use in a communication systemcomprises a network interface configured to obtain, for each of aplurality of communication devices, one or more quality indicatorscorresponding to one or more sub-channel blocks of an orthogonalfrequency division multiplexing (OFDM) communication channel associatedwith the communication device. The network interface is furtherconfigured to select, based on the quality indicators obtained for eachof at least some communication devices of the plurality of communicationdevices, a group of communication devices for orthogonal frequencydivision multiple access (OFDMA) communication, wherein the groupincludes two or more communication devices of the plurality ofcommunication devices. The network interface is additionally configuredto transmit, to the group of communication devices, at least one OFDMAdata unit that includes respective OFDM data units directed to the twoor more communication devices of the group, wherein the respective OFDMdata units are transmitted in respective sub-channel blocks allocated tothe two or more communication devices of the group.

In other embodiments, the apparatus further includes any suitablecombination of one or more of the following features.

The network interface is configured to transmit a sounding packet fromthe first communication device to the plurality of communicationdevices, receive a plurality of respective feedback packets from theplurality of communication devices, wherein the feedback packets includefeedback generated based on the sounding packet, and obtain the one ormore quality indicators for each communication device based on thefeedback packet received from the communication device.

The network interface is configured to transmit a request frame from thefirst communication device to the plurality of communication devices,wherein the request frame requests the communication devices to transmitrespective sounding frames, receive respective sounding packetstransmitted by the communication devices in response to the requestframe, and obtain the one or more quality indicators for eachcommunication device based on the sounding packet received from thecommunication device.

The network interface is configured to receive respective non-soundingdata units transmitted by the communication devices for purposes otherthan sounding the OFDM communication channels associated with thecommunication devices, and obtain the one or more quality indicators foreach communication device based on the non-sounding packet received fromthe communication device.

The network interface is configured to obtain the one or more qualityindicators for each communication device by obtaining one or both of (i)indications of one or more preferred sub-channel blocks for thecommunication device and (ii) indications of order of preference ofmultiple preferred sub-channel blocks for the communication device.

The network interface is further configured to, prior to transmittingthe at least one OFDMA data unit to the group of communication devices,transmit a group management frame to indicate to the communicationdevices of the group that the communication devices are members of thegroup.

The network interface is further configured to allocate, based on thequality indicators obtained for the two or more communication devices ofthe group, the respective sub-channel blocks to the two or morecommunication devices of the group.

The network interface is further configured to after transmitting the atleast one OFDMA data unit to the group of communication devices, obtain,for each of the communication devices of the group, one or more newquality indicators corresponding to one or more sub-channel blocks ofthe OFDM communication channel associated with the communication device,allocate respective sub-channel blocks to the communication devices ofthe group based on the new quality indicators, and transmit at least oneadditional OFDMA data unit that includes respective OFDM data unitsdirected to the two or more communication devices of the group, whereinthe respective OFDM data units are transmitted in respective sub-channelblocks allocated to the two or more communication devices based on thenew quality indicators.

In yet another embodiment, a method for simultaneously communicatingwith multiple communication devices in a communication network includesobtaining, at a first communication device for each of two or moresecond communication devices in a group of second communication devicesfor orthogonal frequency division multiple access (OFDMA) communication,one or more quality indicators corresponding to one or more sub-channelblocks of an orthogonal frequency division multiplexing (OFDM)communication channel associated with the second communication device.The method also includes allocating, based on the quality indicatorsobtained for each of at least some of the two or more secondcommunication devices of the group, respective sub-channel blocks torespective second communication devices of the group. The methodadditionally includes transmitting at least one orthogonal frequencydivision multiple access (OFDMA) data unit that includes respective OFDMdata units directed to the two or more communication devices of thegroup, wherein the respective OFDM data units are transmitted inrespective sub-channel blocks allocated to the two or more communicationdevices of group.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

Obtaining, at the first communication device for each of two or moresecond communication devices in a group of second communication devicesfor OFDMA communication, one or more quality indicators corresponding toone or more sub-channel blocks of the OFDM communication channelassociated with the second communication device comprises transmitting asounding packet from the first communication device to the two or moresecond communication devices, receiving, at the first communicationdevice, a plurality of respective feedback packets from the two or moresecond communication devices, wherein the feedback packets includefeedback generated based on the sounding packet, and obtaining the oneor more quality indicators for each second communication device based onthe feedback packet received from the second communication device.

Obtaining, at the first communication device for each of two or moresecond communication devices in a group of second communication devicesfor OFDMA communication, one or more quality indicators corresponding toone or more sub-channel blocks of the OFDM communication channelassociated with the second communication device comprises transmitting arequest frame from the first communication device to the two or moresecond communication devices, wherein the request frame requests thesecond communication devices to transmit respective sounding frames tothe first communication device, receiving, at the first communicationdevice, respective sounding packets transmitted by the two or moresecond communication devices in response to the requests frame, andobtaining the one or more quality indicators for each secondcommunication device based on the sounding packet received from thesecond communication device.

Obtaining, at the first communication device for each of two or moresecond communication devices in a group of second communication devicesfor OFDMA communication, one or more quality indicators corresponding toone or more sub-channel blocks of the OFDM communication channelassociated with the second communication device comprises receiving, atthe first communication device, respective non-sounding data unitstransmitted by the two or more second communication devices for purposesother than sounding the OFDM communication channels associated with thesecond communication devices, and obtaining the one or more qualityindicators for each second communication device based on thenon-sounding packet received from the second communication device.

Obtaining, at the first communication device for each of two or moresecond communication devices in a group of second communication devicesfor OFDMA communication, one or more quality indicators corresponding toone or more sub-channel blocks of the OFDM communication channelassociated with the second communication device comprises obtaining, foreach second communication device one or both of (i) indications of oneor more preferred sub-channel blocks for the second communication deviceand (ii) indications of order of preference of multiple preferredsub-channel blocks for the second communication device.

The method further includes after transmitting the at least one OFDMAdata unit to the group of second communication devices, obtaining, foreach of the second communication devices of the group, one or more newquality indicators corresponding to one or more sub-channel blocks ofthe OFDM communication channel associated with the second communicationdevice, allocating respective sub-channel blocks to the secondcommunication devices of the group based on the new quality indicators,and transmitting at least one additional OFDMA data unit that includesrespective OFDM data units directed to the two or more secondcommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more second communication devices based on the new qualityindicators.

In still another embodiment, an apparatus for use in a communicationsystem comprises a network interface configured to obtain, for each oftwo or more communication devices in a group of communication devicesfor orthogonal frequency division multiple access (OFDMA) communication,one or more quality indicators corresponding to one or more sub-channelblocks of an orthogonal frequency division multiplexing (OFDM)communication channel associated with the communication device. Thenetwork interface is additionally configured to allocate, based on thequality indicators obtained for each of at least some of the two or morecommunication devices of the two or more communication devices,respective sub-channel blocks to respective communication devices of thegroup. The network interface is further configured to transmit at leastone orthogonal frequency division multiple access (OFDMA) data unit thatincludes respective OFDM data units directed to the two or morecommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more communication devices of group.

In other embodiments, the apparatus further includes any suitablecombination of one or more of the following features.

The network interface is configured to transmit a sounding packet to thetwo or more communication devices, receive a plurality of respectivefeedback packets from the two or more communication devices, wherein thefeedback packets include feedback generated based on the soundingpacket, and obtain the one or more quality indicators for eachcommunication device based on the feedback packet received from thecommunication device.

The network interface is configured to transmit a request frame to thetwo or more communication devices, wherein the request frame requeststhe communication devices to transmit respective sounding frames,receive respective sounding packets transmitted by the two or morecommunication devices in response to the requests frame, and obtain theone or more quality indicators for each communication device based onthe sounding packet received from the communication device.

The network interface is configured to receive respective non-soundingdata units transmitted by the two or more communication devices forpurposes other than sounding the OFDM communication channels associatedwith the communication devices, and obtain the one or more qualityindicators for each communication device based on the non-soundingpacket received from the communication device.

The network interface is configured to obtain the one or more qualityindicators for each communication device by obtaining one or both of (i)indications of one or more preferred sub-channel blocks for thecommunication device and (ii) indications of order of preference ofmultiple preferred sub-channel blocks for the communication device.

The network interface is further configured to after transmitting the atleast one OFDMA data unit to the group of communication devices, obtain,for each of the communication devices of the group, one or more newquality indicators corresponding to one or more sub-channel blocks ofthe OFDM communication channel associated with the communication device,allocate respective sub-channel blocks to the communication devices ofthe group based on the new quality indicators, and transmit at least oneadditional OFDMA data unit that includes respective OFDM data unitsdirected to the two or more communication devices of the group, whereinthe respective OFDM data units are transmitted in respective sub-channelblocks allocated to the two or more communication devices based on thenew quality indicators.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for simultaneously communicating withmultiple communication devices in a communication network, the methodcomprising: receiving, at a first communication device, soundingfeedback packets from a plurality of second communication devices,wherein each sounding feedback packet includes (i) beamforming feedbackto be used by the first communication device for beamforming to thecorresponding second communication device and (ii) one or more qualityindicators corresponding to one or more sub-channel blocks of anorthogonal frequency division multiplexing (OFDM) communication channelassociated with the corresponding second communication device;selecting, at the first communication device based on the one or morequality indicators received from each of at least some of the secondcommunication devices, a group of second communication devices fororthogonal frequency division multiple access (OFDMA) communication,wherein the group includes two or more second communication devices ofthe plurality of second communication devices; and transmitting, fromthe first communication device to the group of second communicationdevices, at least one OFDMA data unit that includes respective OFDM dataunits directed to the two or more second communication devices of thegroup, wherein the respective OFDM data units are transmitted inrespective sub-channel blocks allocated to the two or more secondcommunication devices of the group.
 2. The method of claim 1, furthercomprising prior to receiving the sounding feedback packets,transmitting a sounding packet from the first communication device tothe plurality of second communication devices, wherein the soundingfeedback packets are transmitted by the plurality of secondcommunication devices in response to receiving the sounding packet. 3.The method of claim 1, wherein the one or more quality indicatorscorresponding to one or more sub-channel blocks of the OFDMcommunication channel associated with the second communication deviceinclude one or both of (i) indications of one or more preferredsub-channel blocks for the second communication device and (ii)indications of order of preference of multiple preferred sub-channelblocks for the second communication device.
 4. The method of claim 1,further comprising, prior to transmitting the at least one OFDMA dataunit to the group of second communication devices, transmitting a groupmanagement frame to indicate to the second communication devices of thegroup that the second communication devices are members of the group. 5.The method of claim 1, further comprising allocating, based on thequality indicators obtained for the two or more second communicationdevices of the group, the respective sub-channel blocks to the two ormore second communication devices of the group.
 6. The method of claimof claim 5, further comprising: after transmitting the at least oneOFDMA data unit to the group of second communication devices, obtaining,for each of the second communication devices of the group, one or morenew quality indicators corresponding to one or more sub-channel blocksof the OFDM communication channel associated with the secondcommunication device, allocating respective sub-channel blocks to thesecond communication devices of the group based on the new qualityindicators, and transmitting at least one additional OFDMA data unitthat includes respective OFDM data units directed to the two or moresecond communication devices of the group, wherein the respective OFDMdata units are transmitted in respective sub-channel blocks allocated tothe two or more second communication devices based on the new qualityindicators.
 7. An apparatus for use in a communication system, theapparatus comprising: a network interface comprising one or moreintegrated circuits configured to receive sounding feedback packets froma plurality of communication devices, wherein each sounding feedbackpacket includes (i) beamforming feedback to be used for beamforming tothe corresponding communication device and (ii) one or more qualityindicators corresponding to one or more sub-channel blocks of anorthogonal frequency division multiplexing (OFDM) communication channelassociated with the corresponding communication device; select, based onthe one or more quality indicators received from each of at least somecommunication devices of the plurality of communication devices, a groupof communication devices for orthogonal frequency division multipleaccess (OFDMA) communication, wherein the group includes two or morecommunication devices of the plurality of communication devices; andtransmit, to the group of communication devices, at least one OFDMA dataunit that includes respective OFDM data units directed to the two ormore communication devices of the group, wherein the respective OFDMdata units are transmitted in respective sub-channel blocks allocated tothe two or more communication devices of the group.
 8. The apparatus ofclaim 7, wherein the one or more integrated circuits are furtherconfigured to: prior to receiving the sounding feedback packets,transmit a sounding packet to the plurality of communication devices,wherein the sounding feedback packets are transmitted by the pluralityof communication devices in response to receiving the sounding packet.9. The apparatus of claim 7, wherein the one or more quality indicatorscorresponding to one or more sub-channel blocks of the OFDMcommunication channel associated with the communication device includeone or both of (i) indications of one or more preferred sub-channelblocks for the communication device and (ii) indications of order ofpreference of multiple preferred sub-channel blocks for thecommunication device.
 10. The apparatus of claim 7, wherein the one ormore integrated circuits are further configured to, prior totransmitting the at least one OFDMA data unit to the group ofcommunication devices, transmit a group management frame to indicate tothe communication devices of the group that the communication devicesare members of the group.
 11. The apparatus of claim 7, wherein the oneor more integrated circuits are further configured to allocate, based onthe quality indicators obtained for the two or more communicationdevices of the group, the respective sub-channel blocks to the two ormore communication devices of the group.
 12. The apparatus of claim 11,wherein the one or more integrated circuits are further configured to:after transmitting the at least one OFDMA data unit to the group ofcommunication devices, obtain, for each of the communication devices ofthe group, one or more new quality indicators corresponding to one ormore sub-channel blocks of the OFDM communication channel associatedwith the communication device, allocate respective sub-channel blocks tothe communication devices of the group based on the new qualityindicators, and transmit at least one additional OFDMA data unit thatincludes respective OFDM data units directed to the two or morecommunication devices of the group, wherein the respective OFDM dataunits are transmitted in respective sub-channel blocks allocated to thetwo or more communication devices based on the new quality indicators.